Page:Popular Science Monthly Volume 92.djvu/105

 Launching a Bridge-Pier Caisson

The caisson was built on a scow, on which it was towed to position and from which it slid into the water

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���� ��The caisson ready to be towed out to its final resting place as a sup- port for one of the con- crete piers of the bridge

��/%N interesting en- r\ gineering feat was performed recent- ly at Manila, P. I., when a timber caisson for one of the concrete piers of the Jones bridge was launched in half an hour.

The caisson was built on a scow which could be tilted so the caisson could slide off into the water and be towed to its loca- tion where it was to be sunk and the con- crete pier built inside of it. The caisson was 100 feet long, 35 feet wide and 36 feet high, longer and wider than an ordi- nary city house. Three feet above the

���The scow was divided by a bulk- head so that water could be ad- mitted into one side to make the scow list as the caisson slid off

��The only lines neces- sary were those to keep the caisson from float- ing down-stream and the towing lines

lower edge of the caisson was a 4-inch calked plank floor supported by in- verted timber trusses, which in turn rested on timber sills bolted to the upper edge of the con- crete walls. The floor and trusses were designed to withstand water pressure during flota- tion. When all was ready, the valves on the midstream side of the scow were opened. When the caisson began to slide, the scow was pushed from underneath the structure. It was manned at once and sunk by opening valves in the eight compartments into which it was divided.

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��Twenty-three minutes after opening the valves, the list was fifteen degree? and the caisson slid into the water

��Due to the low center of gravity the cais- son righted itself quickly and finally rested on an even keel in eight feet of water

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